This invention relates to a repeat control apparatus for a serial interface keyboard apparatus, which is adapted to cause a key code input via a key operation on a keyboard to be sent in a bit serial mode to a host unit, such as a terminal main unit.
A conventional serial interface keyboard apparatus 1 of this type includes a timer 2, as shown in FIG. 1. The repeat time interval of the key required in a repeat operation is determined by the time count control of the timer. The apparatus of FIG. 1 comprises a host unit (a terminal main unit) 3, a keyboard interface controller KB 4 for performing serial interface control with respect to the keyboard apparatus 1, a key matrix section KEY 5, a keyboard controller KBC 6 for performing serial interface function, and a signal line 7 connected between the keyboard apparatus 1 and the host unit 3.
The repeat control operation of the conventional keyboard apparatus 1 may be explained as follows, with reference to FIG. 2. Upon depression of a key (with key code XX.sub.H, a hexadecimal) on the key matrix section 5 of the keyboard apparatus 1, the code XX.sub.H belonging to the key is transferred in a bit serial mode to the host unit 3, through the signal line; and, at the same time, the timer 2 starts to effect a time count operation. When the timer 2 counts, e.g., 500 msec., a repeat operation is started, i.e., a repeat operation is performed for every 100 msec.
However, such a conventional repeat control means has a drawback, in that the keyboard apparatus 1 requires a timer 2 for repeat control, thus complicating the hardware configuration. Furthermore, since the repeat time interval (500 msec., 100 msec. in FIG. 2) is fixed by the hardware, it is not possible to arbitrarily change the repeat time interval without changing the associated hardware. The host unit 3 cannot distinguish the keyed-in code, when the repeat operation is being carried out by the operation of the timer, from the keyed-in code when an operator performs input operations a number of times. It is therefore impossible to distinguish a repeatable keyed-in code from the keyed-in code which is not repeatable (a specific function key). Thus, the conventional apparatus includes disadvantages which are both structural and functional.